texts: How official is TNO 486958, 2014 MU69's new name Arrokoth?

texts:
The Trans-Neptunian object 486958 or 2014 MU69 has had several designations and nicknames. According to Phys.org's NASA renames faraway ice world 'Arrokoth' after backlash

  Ultima Thule, the farthest cosmic body ever visited by a spacecraft, has been officially renamed Arrokoth, or "sky" in the Native American Powhatan and Algonquian languages, following a significant backlash over the old name's Nazi connotations.

Wikipedia's 486958 Arrokoth says

  When Arrokoth was first observed, it was labelled 1110113Y, nicknamed "11" for short. Its existence as a potential target of the New Horizons probe was announced by NASA in October 2014 and it was unofficially designated as "Potential Target 1", or PT1. Its official designation, 2014 MU69 (a provisional designation indicating that it was the 1745th object assigned one for the second half of June 2014), was assigned by the Minor Planet Center (MPC) in March 2015, after sufficient orbital information was gathered. After further observations refining its orbit, it was given the permanent minor planet number 486958 on 12 March 2017.

Questions:

Exactly how official is the new name Arrokoth? Is there further approval necessary or are 486958 and 2014 MU69 and Arrokoth recognized equally as official names?
Are 486958 and 2014 MU69 and Arrokoth all likely to be used interchangeably in astronomical literature from now on, or will one designation emerge as the most commonly used name?


texts: Shouldn't tidal locking be impossible for a satellite that has a considerably eccentric orbit?

texts:
This popped up into my mind just now. The Moon is tidally locked to Earth, and also has a significantly eccentric orbit. This means that its orbital velocity near periapsis is considerably faster than its orbital velocity at apoapsis.
Thus, for the Moon to always show one side to Earth, its rotation around its own axis has to slow down and speed up depending on where it is in its orbit, but doesn't that violate the law of conservation of angular momentum? And if its rotation around its axis was constant then it would get out of sync and not be tidally locked, no?


texts:
In literature about the instrumentation of radio astronomy, I frequently come across a type of mixer described as "2SB".  I'm familiar with single-sideband (SSB) and double-sideband (DSB) mixers, but I have never studied a 2SB mixer.

What is a 2SB mixer and how does it compare to a DSB mixer?  Ideally, I would also like to know of formal references that directly address the topic for further reading.


texts: How would one calculate the synodic period of the Earth and an elliptical orbit?

texts:
For example, when would someone with a telescope be able to see Starman and his Roadster (when will the Tesla roadster's elliptical orbit cross ours again, and how would that be calculated?)

For two circular orbits, I understand this is given by $$\frac{1}{S} = \frac{1}{T_2} - \frac{1}{T_1} $$ .


texts: What is the difference between the two terms named "Eccentricity" and "Ellipticity"?

texts: I don't get the difference between the two terms named "Eccentricity" and "Ellipticity", especially, in astronomy. I understand eccentricity as a measure of the curvature of a orbit but what is ellipticity?


texts: Why do objects burn when they enter earth's atmosphere?

texts: Why do all objects burn when they enter our atmosphere? is this because of our atmosphere composition? and does this happen on other planets as well?


texts:
Fleming 1 is an unusual planetary nebula situated in the Centaurus constellation.

Yet it is not clear after who it was named


texts: Does the critical density of the Universe also include Dark Energy?

texts:
It is often said that it seems that the Universe is quite close to critical density (for example https://astronomy.swin.edu.au/cosmos/C/Critical+Density).
Does this include Dark Energy as well (apart from Dark matter and Baryonic matter)?


texts: Can dark energy or dark matter affect black holes

texts: I was wondering if black holes are the greatest force of gravity how does other highly spoken about concepts such as dark energy or dark matter compare. Can a black hole absorb dark energy or dark matter? I though dark matter held galaxies together. If a black hole could absorb the dark matter would that be a problem: i.e. the universe getting smaller?


texts:
The vast majority of energy from a supernova is emitted as neutrinos and high-energy radiation, both of which being invisible to the naked eye. Yet a supernova can outshine its galaxy in the visible spectrum for weeks.

How is a supernova generating so much visible light that nuclear fusion pales in comparison?
What is the ratio of visible and invisible energy emitted by a supernova, and how does it compare to stars' normal operation?


texts:
I've heard that the more an object spins, the less of a true sphere it is.
Using this logic most of neutron stars would be far from spherical,in general what shape are most neutron stars?


texts: What is the gaseous-to-rocky ratio of exoplanets?

texts:
Around the Sun, there are as many gaseous planets (Jupiter, Saturn, Uranus and Neptune) as there are rocky planets (Mercury, Venus, Earth and Mars).

Do other stars have similar gaseous-to-rocky ratios among their planets? For any given stellar system, are there typically as many gaseous planets as there are rocky planets? Or do most stars have either mostly gas giants or mostly rocky planets, making our own Solar system an exception? Perhaps we need more data to conclude, since we often have mass or radius, but not both for exoplanets?


texts:
As I stated in the title, I saw this ball of light moving across the sky. It wasn't moving fast, but it wasn't moving slow.

So, I was sitting my dad's car when I looked through the windshield and at the sky to see a ball of (white) light moving across the sky. It wasn't small like the other stars, it was actually really big compared to them. It was kind of quickly moving across the sky before it faded. I thought it was a pane but the light didn't re-appear.  I then thought it was a shooting star, but after some research, I realised I was once again wrong.

I've seen this before, yet I still can't find out what it is.

Maybe some of you know what it is..?


texts: How could a neutron star collapse into a black hole?

texts:
White dwarfs usually do not collapse, as they have electron degeneracy pressure due to the Pauli exclusion principle. However, if one accretes mass beyond the Chandrasekhar limit, it is energetically favorable for the electrons to combine with protons and form neutrons. This gives us a neutron star.

However, neutron stars usually do not collapse into black holes due to neutron degeneracy pressure. How is it possible that beyond the LOV limit, the Pauli exclusion principle no longer prevents the collapse? Shouldn't it still prevent neutrons, which are fermions, from being compressed together any further?

I've seen answers involving quark stars, but those are purely hypothetical. What is the most accepted explanation for this?


texts: Saturn observation : how to calculate requirements for Parallax method

texts:
In September, Saturn is 9.9au away from Earth. If we use the parallax method, what should be the base line between the two people?

So I know that $D = B / \theta$, but how do I find out theta? I'm pretty sure the answer is pretty obvious, but my mind really is not working right now, so any help is appreciated

Thank you in advance.


texts: Can a star emit heat but no visible light?

texts: Can a star emit enough heat to allow human life on its planets, however emit no visible light? If so, what problems would this pose?


texts: What shape do satellites trace as they wobble in orbit around another body?

texts:
What shape does the center of gravity of a satellite trace in 3-d space as it wobbles in orbit around another body? How is this shape modeled geometrically? Is it a topological torus? Is it feasible/useful to cross-section this shape at a right angle to the orbital path and graph the probability distribution of pathways in 2-d within the cross-section? Has this been done for the Moon around the Earth for example? That's a lot of questions but I think they're all closely related and the point is to obtain a conceptual model of orbit paths.
EDIT: The answers diverge so let me specify the question further. I have a vague recollection of the application of Lorenz Attractors to planet satellite paths. (This problem set is by the way one of the historical bases of chaos theory.) However, Lorenz Attractors are generally represented as full orbits in 3-d space, like so:

I'm trying to get to the 2d representation, if it exists, i.e. a 2d cross-section of the orbit paths, which probably do not fit in a disc, but in a torus, unlike the above image generated by a simple model. Might this cross-section  look like a Hénon map?


texts:
I had a meeting in the evening and thought of grabbing a snack before that. I stepped out of the office along with a colleague. He was on his phone and I was simply staring at the sky wishing it would rain. Although there was no trace of a cloud, however, what I saw was beyond what I expected and could ever imagine.

I saw three stars aligned in an inverted triangle, moving at a decent speed away from each other. For a moment I didn't believe what I was seeing. I quickly called my colleague and asked him if he could see something moving in the sky. Well, we both were astonished as we saw the stars moving away from each other and changing there position in the sky.

After that evening I went back home a was awake till 4 am sitting at the terrace staring at those three stars, wishing them to move again. It's been three days and the stars are still in the same position.

Yes, I can detect those three stars as they were right above the north star.

In these three days, I have done a bunch of research on satellite, shifting stars, supernova and so on but nothing could explain what we saw.

I would love to know if anyone had the same experience as us.


texts: Neutrino interaction with dense molecular structures

texts: Would dense molecular structures on heavier planets (crystalline or other compounds which are generally unknown to us) allow neutrinos to pass through as easily as on Earth?


texts: What is the name of a device for detecting moving objects?

texts:
A while ago I saw a report on TV, where an astronomer described a device that was used for detecting movement of stellar objects (mainly asteroids, I think) before the age of computers. In order to detect such a movement, two photos of the region of interest were made, through a telescope, with a certain delay between these photos.

Afterwards, the photos have been placed into that device. The device had some sort of "peephole" through which one could see one of the photos, and some sort of lever/switch to quickly toggle between the photos - either by flipping them, or by tilting a mirror to show either of the photos.

Objects that had moved between the photos (relative to the other, "fixed" objects) could thus quickly and easily be identified with the naked eye, because they appeared as dots jumping forth and back when toggling between the photos.

Does anybody know the name of this device, or a more detailed technical description?


texts: In which two constellations, were the two gravitational wave events of 2016?

texts:
As best as is known, what is the latest thinking on in the issue of,

in which constellation was GW150914, and in which constellation was GW151226?

(That is to say, within the large uncertainty, as best as is known in what direction is the likely center of that uncertainty?)


texts: Total angular momentum in system of binary brown dwarfs on wide orbit from primary star

texts:
I want to calculate the total angular momentum of a system in which two brown dwarfs are orbiting one another (P ~ 10 years), and this system is stably orbiting a third primary ZAMS star (P ~ $10^4$ years). I was thinking of approaching this question from a Hamiltonian mechanics perspective, but the problem doesn't become easier in the rotating reference frame.

Let A denote the primary star, and B,C denote the two components of the binary. I was thinking the angular momentum would simply be the sum of rotational (S) and orbital angular (L) momentums:
$$
L_{tot} = S_{A} + S_{B} + S_{C} + L_{BC} + L_{A+BC}
$$

However, I am both worried that I am partially "double counting" with the last term and I don't really know how to treat the last term. Do I treat BC like a single mass at their barycenter?

If there is a Hamiltonian method to approach this problem, I am all ears.

The question I am actually concerned with is what would the rotation rate of the primary star be if the total angular momentum of the system was in the primary star? But I would really just like an accurate description of the angular momentum of the system to do this.


texts: Does space not make sound, or can we just not hear it?

texts:
This is a question regarding sound waves and space.

I know that sound waves must travel through a medium "air", enter our brains, and then we can decipher what exactly the sound is.

But in space, there is no air, and so does that mean that no sound waves are being produced, or that there are waves, but we cannot hear them because they never reach us

And how can we tell? We cannot "hear" space, so who says its because theres no air, rather then just because "its not being produced in the first place?"


texts: Must time pass more slowly, relative to our inertial reference frame, inside galaxies that are currently located at half way to the Hubble Horizon?

texts:
Trying to understand simultaneity of events and time-dilation on a Universe scale, I would like to know must time pass more slowly, right now, relative to our current inertial reference frame, inside galaxies that are currently located at say "half way" to the Hubble Horizon because such galaxies are moving at around .5c? In this case no acceleration was experienced to generate the speed difference, just space expansion.
I can't see how it could not be true, (I think the Lorentz transformation still hold) but I think if it is true it leads to problems.


texts: How do I calculate B-V to make a Hertzsprung Russell diagram?

texts:
I am reading my textbooks and a few "Astro101" websites, but I cannot find a final answer to this:

In the $B-V$ colour index that is plotted in an H-R diagram, are $B$ and $V$ the (observed) apparent magnitudes, or should they be corrected for extinction first, i.e. with known $A_V$ and $A_B$ values?


texts: Parent stars of our Sun - Where are its remains?

texts:
This is in a way related to this question.

Question is: Our star is third generation star, which is explained by existing Barium. That Barium was created by other stars. Now, those stars must have been Supernova. When they exploded, it was either a neutron star or a black hole.
Where is that Neutron star or black hole?


texts: Are the Venusian "continents" likely to have existed before the global resurfacing event?

texts: A topographic map of the surface of Venus shows the large highland areas Ishtar Terra, Aphrodite Terra and Lada Terra that have occasionally been described as "continents", plus various other smaller regions such as Beta Regio. Are these "continents" likely to have existed before the global resurfacing event, or is the topography of the planet likely to have been completely altered?


texts: Were magnetic monopoles created before, during or after inflation?

texts: In the case that magnetic monopoles exist, when were they created? I thought that all particles were created after inflation, but I've read some comments recently that hint at a pre-inflationary creation of magnetic monopoles.


texts: What is the difference between emission line and recombination line?

texts: When an electron jumps from higher level to lower level a photon is emitted. This is seen as an emission line. But what exactly is a recombination line? I found them similar. Can you please tell me what's the difference between these two?


texts: This morning at 6:12 am looking south from Georgetown, Texas, there was a brief very bright stationary object what appeared to be a star that once I saw it within the next few seconds quickly vanished.  Did not appear to be other than a stationary object.  What was it?


texts: What effect does the Moon have on the near Earth asteroid population?

texts:
Does the big (0.012 Earth masses) Moon of Earth clear away NEAs, Earth orbit crossing asteroids, in a significant way? Venus and Mars don't have large moons, do they therefore have larger or smaller population of near asteroids than Earth would have if it were in the same orbit?

The outer planets have large moons, but also lots of captured asteroids, trojans and centaurs. Does a large moon even help gathering such objects, rather than ejecting them? Moonless Mercury and Venus seem to be pretty clean.


texts:
The end of the relativistic jet that emerges from M87 looks curved like a hook. See here:

Data from the VLA array show more of the jet: at the far end, the jet makes a complete 180 degree turn backwards toward the galaxy it emerges from.

What forces the jet to make such a drastic turn around?


texts: Why is solar corona in visible light filamentary?

texts:
There is a video on YouTube (unfortunately in Czech) where Miloslav Druckmüller talks about structure of the solar corona in visible light. He explains that the filaments, clearly visible on his photographs, delineate magnetic field lines - the light coming from photosphere is scattered by free electrons which move along magnetic field lines.

What I don't understand (and he doesn't explain) how this explains the filamentary structure.
Why is the scattered light visible only along some field lines and not in between them?


texts: Where is the Moon for the last five or six days?

texts: The date today is March 18th 2021 Thursday it's 6:00 p.m. I'm in the area of Sarasota-Bradenton Florida. I haven't seen the moon and it's been clear skies for roughly the last five or six nights... I see all the consolation of the Stars where they're supposed to be but I cannot find the Moon. It makes me nervous and I'd like to know why?


texts:
Some planets, specifically Jupiter, Saturn, Uranus, and Neptune in our solar system, have planetary rings.

Why do some planets have rings? How are they made and from what? Most importantly, will I be able to observe the rings on any planet with an amateur telescope?


texts: Are 3D coordinate data from Sloan DSS-III available & easily accessible to non-pros?

texts:
Of course the newly announced SDSS-III data and maps from the Sloan Digital Sky Survey with 1.2 million objects, along with all previous data sets are openly available, and I'm sure there are many tools to access, work with, and view the data.

What would be the simplest way to extract a list of coordinates of galaxies in order to just try to visualize it on my own? There may be visualization tools also, if you want to add a link that would be great, but this question is about getting a list of coordinates so I can look at density or even try to plot one dot per galaxy in some slice.

I'm guessing the coordinates might be available in RA, dec, and redshift, and possibly also some calculated/inferred x, y, z.

I use python, but I'm not familiar with AstroPy yet, so if it can be done, albeit inefficiently and/or inaccurately by my writing a straightforward python script on my laptop, that would be the most helpful answer.

edit: if doing this in AstroPy is failry easy, I do have an Anaconda installation, and therefore already have at least a basic AstroPy installation.

Here is a graphic (below), from here in Phys.org attributed there to Daniel Eisenstein and SDSS-III.

Another graphic (below), from here in Phys.org attributed there to Jeremy Tinker and SDSS-III.


texts: What happens for a "closed" universe without any content?

texts:
Let an universe with no content and positive curvature.
Friedmann-Lemaître equation
$$H^2=\frac{8\pi G}{3}\left(\rho_m+\rho_r+\rho_{\Lambda}\right)-\frac{k\, c^2}{a^2},$$
where $a$ corresponds to the scale factor of Friedmann-Lemaître-Robertson-Walker Metric, and the $\rho$ to the density of the contents,
will become $$H^2=-\frac{\, c^2}{a^2},$$ as positive curvature (closed universe) corresponds to $k=+1$.

So, as $H=\frac{\dot{a}}{a}$ with $\dot{a}=\frac{da}{dt}$,

$$da=\pm i \, c \, dt$$

$$a(t)=\pm i \, c \, t + cst$$

what am I doing wrong ?


texts: How do I get from Star Atlas to real life?

texts:
This question is about finding the elevation and bearing of a given star at a particular time at Latitude 52N.

I look up the RA and Declination of my star. How do I calculate its bearing and elevation at hourly intervals?


texts: Earth-Centered Earth-Fixed coordinates with respect to heliocentric coordinate system at vernal equinox

texts:
I am trying to calculate the position of a point on the Earth's surface with respect to the Sun's center at a certain date and time.
For what I am trying to do it is OK to ignore precession of Earth's orbit and precession, nutation and polar motion of the rotating Earth.

Lets say that I have coordinate system centered at the Sun $X,Y,Z$, where the $X$ axis points at the point of vernal equinox, the $XY$ plane is the plane of Earth's orbit around the Sun, the $Z$ axis pointing toward the ecliptic north pole and then $Y$ completes the right-handed system.

So far I've been able to find the following orbital elements at the epoch J2000:

$a=1 \ \mathrm{AU}$ — major radius

$\bar{\lambda_0}=100.47^\circ$ — mean longitude at epoch

$e=0.01673$ — eccentricity

$I=0^\circ$ — inclination to the ecliptic

$\bar{\omega}=102.93^\circ$ — longitude of perihelion

$T=1 \ \text{year}$ — orbital period

$\frac{m}{M}=3.039\times 10^{-6}$ — planetary-solar mass ratio

Now knowing this I could determine the orbit of the Earth at a certain date, however I am unable to determine Earth's orientation.
Lets say that we have ECEF coordinate $x,y,z$ system centered at Earth's center of mass with the $z$ axis pointing toward the north pole (we can assume that it coincides with Earth's rotational axis), the $x$ axis pointing toward the intersection of the prime meridian and the equator and then $y$ completing the right-handed system.

At the point of vernal equinox by definition the equatorial plane crosses the center of the sun.Knowing this and the axial tilt of $~23.44^\circ$ of the Earth's rotational axis I can determine the $z$ axis and $xy$ plane with respect to $X,Y,Z$ coordinates but I cannot determine the exact positions of $x$ and $y$ axes which I need.

I searched a lot for data showing me the orbital elements at certain epoch AND the exact orientation of the Earth ($x,y,z$ coordinates expressed as $X,Y,Z$ at the vernal equinox) so that I can use it for my calculations but I didn't succeed. From all the things that I found I am still unable to tell what the orientation of the Earth is at certain point so I can't really determine the position of certain point on its surface at certain time with respect to the Sun.

I assume that I am missing something or that I have some fault in my approach since I am complete noob at astronomy and I've never dealt with this before I had to find a way to perform this calculation. I will take any suggestions if there is a better way to solve the initial problem that I am trying to solve or if there is a place where I can find the data that I need.


texts: Black hole darkness a result of gravity or temporal distortion?

texts:
Please correct me if I am wrong as I may have made some incorrect assumptions.

Okay so we know that at some stage of "nearness to a black hole", light is no longer reflected back at us from the black hole itself. Some scientists have proposed the speed of light and it's relationship to relativity is natures way of adjusting the rate at which time passes seemingly to disallow "weirdness that could result" .. for example the fast moving object would become more massive.

We also know that the mass of the black hole causes a nearby observer to behave as if he/she were moving at incredible speeds and subsequently slows time for the observer "relatively speaking of course".

I realize that from the perspective of the observer light is traveling to and away from him/her at it's normal rate even though effectively the observer is traveling very fast. Imagine however what would happen to the frequency of the light. The red/blue shift would undoubtedly be obscene.

Since we here on earth are "relatively speaking" experiencing time passing at our normal "earth rate". I can't help but imagine that immense gravity near a black hole is distorting time and its darkness is a result of either extreme red/blue shift or the light is somehow phased or altered by the temporal distortion. Yes gravity is the origin of the darkness but is the direct cause or an indirect relationship where the rate of time passing is the culprit?


texts: Why would astronomers want to eclipse the Sun?

texts:
I've heard that some astronomers are building an artifical solar-eclipse ship, that should help us to dim the diffraction of the Sun.

Why don't we just wait till night? What is the function of the eclipse-ship really?


texts: Does the shape of a supernova remnant depend on the progenitor star's magnetic field?

texts: The magnetic field activity in a star can be very chaotic and my question is are they somehow related?


texts: What are the characteristics of solid carbon dioxide on the Martian poles?

texts:
When carbon dioxide forms on Mars is it like ice or snow? How dense is newly formed solid carbon dioxide? Would more carbon dioxide form inside a pit vs a flat plain?

How thick or deep does solid carbon dioxide accumulate on Mars?

https://space.stackexchange.com/questions/31724/martian-carbon-dioxide-turbine-oxygen-generator


texts: Relatable comparison of VY Canis Majoris to the Sun?

texts: I was trying to describe how vast the largest known star is to someone and felt I wasn't quite able to relate the scale difference. I know it's roughly 1500 times larger than the sun. Anyone know of a good analogy?


texts: Sloan Digital Sky Survey (SDSS) HDU `or_mask` - what does it mean exactly?

texts:
I'm looking at the Sloan Digital Sky Survey data. I'm primarily using the flux data, from the documentation I see the first extend (HDU 1) has flux, loglam, ivar, and_mask, or_mask, etc.

There's been a lot of confusion here about what the or_mask is doing exactly, and the documentation hasn't been extremely clear.

My understanding so far is that the or_mask tells me when a particular pixel was flagged in one of many ways possible. I've understood from various random sources that this means the pixel is "bad" somehow. I haven't yet figured out how to know exactly "why" it is bad, my working assumption is that the possibilities are numerous, that there are many fields that have flags that might answer that question.

My primary question: Is every flux value with a non-zero or_mask inherently untrustworthy?

About 80% of pixels have a non-zero or_mask value, particularly on the bluer end of the spectrum.

Or is the or_mask telling me more broadly that there's a flag somewhere, not necessarily even with the flux data, that I might want to consider?

HDU 1 (extname COADD): Coadded Spectrum from spPlate

Binary table with columns:
                        Required  Columns
Name      Type      Comment
flux      float32   coadded calibrated flux [10-17 ergs/s/cm2/Å]
loglam    float32   log10(wavelength [Å])
ivar      float32   inverse variance of flux
and_mask  int32     AND mask
or_mask   int32     OR mask
wdisp     float32   wavelength dispersion in pixel=dloglam units
sky       float32   subtracted sky flux [10-17 ergs/s/cm2/Å]
model     float32   pipeline best model fit used for classification and redshift


texts: How to calculate planetary positions hundreds or thousands of years ago

texts:
Wondering how to calculate the following in a general way:

Sunrise/sunset
Equinoxes/solstices
Moon phases
Planetary positions

For hundreds to thousands of years ago. Wondering what the calculation is, or where I go about figuring it out.

I would like to be able to say, in 1541 on Jan 1 the sun rose at x time, Jupiter was in y position, etc.


texts: Feasibility of radioastronomy in densely populated areas

texts:
In general, radioastronomy as well as optical astronomy depend on a good SNR. This meant to position telescopes as far as possible from noise sources. Optical telescopes were built at elevated points to reduce diffuse light from Rayleigh scattering. Radio telescopes were put into service at similar locations benefiting from shadowing effects of surrounding mountains.

Even radio quiet zones were established mainly to protect large single dish antennas.

With rising computation power available interferometry gained momentum. There are interferometers consisting of very cheap components relying on massive computing power to retrieve the signals from noise. Still, professional interferometers like MWA or LOFAR are built as far as possible from civilisation.

I wonder, if evolvement of algorithms and computing power might it make feasible to build interferometers close or even within more densely populated areas.

Of course one needs to increase the number of antennas in comparison to remote areas to reach a comparable SNR but this might be outweighted by the reduction of cost for installation and service.


texts: How would we be able to detect Exomoons? We detect exoplanets by seeing if the light gets faint from a star, but could we really use the same method for determining if there is an exomoon around that exoplanet? Thanks for your thoughts and answers!


texts: Why would a planet form a cometlike tail under conditions of weaker rather than stronger solar wind?

texts:
This question is prompted by one posted on the worldbuilding stack exchange:
https://worldbuilding.stackexchange.com/questions/189701/could-this-planets-tail-be-visible
I understand that the ionized gas tails of comets are formed by the effect of solar radiation on the comet followed by a push from the solar wind.
In the article on Venus I found and then an article on a gas giant exoplanet linked in the comments, both planets formed a tail under conditions of low solar wind.  Text and links to these sources below.
http://www.esa.int/Science_Exploration/Space_Science/When_a_planet_behaves_like_a_comet

The observations were made in August 2010 when NASA’s Stereo-B
spacecraft measured a drop in solar wind density to 0.1 particles per
cubic centimetre, around 50 times lower than normally observed; this
persisted for about 18 hours.  As this significantly reduced solar
wind hit Venus, Venus Express saw the planet’s ionosphere balloon
outwards on the planet’s ‘downwind’ nightside, much like the shape of
the ion tail seen streaming from a comet under similar conditions.
“The teardrop-shaped ionosphere began forming within 30–60 minutes
after the normal high pressure solar wind diminished. Over two Earth
days, it had stretched to at least two Venus radii into space,” says
Yong Wei of the Max Planck Institute for Solar System Research in
Germany, lead author of the new findings.

 A giant comet-like cloud of hydrogen escaping the warm Neptune mass exoplanet GJ 436

According to our simulation, the stellar radiation pressure
counterbalances ≲70% of the star’s gravity pull on escaping atoms,
which is much less than in hot Jupiter systems, in which radiation
pressure takes over stellar gravity by factors of 3 to 5 (ref. 20).
The low stellar radiation pressure at GJ 436b allows the formation of
a large coma and tail of escaping atoms, co-moving with the planet
although not gravitationally bounded to it (Fig. 4).

When I think of wind forming a tail I think of a smokestack on a windy day.  More wind = longer tail.  I do not understand why weaker solar wind would allow a planetary tail and stronger would prevent it.


texts: Determine sun azimuth and elevation for shading a window throughout the year

texts:
I was wondering how I could get the sun's azimuth and elevation values to shade a particular window with a roller shutter.

At first I thought azimuth is good enough; of course, it wasn't, as I found out in practice.
While there are calculators to find a and e for a specific location at a certain date, I lack the maths to figure out when the sun will hit a western window.

The window faces 270 deg, I know how far the eaves stick out, and the top and bottom edges of the window (and of course location).

I get the idea the maths will be complicated... however, (it won't matter much) as I want to program this into a controller to operate the shutter.

Any hints appreciated.


texts: Do anti-particle black hole exist and can they evaporate?

texts: I know that virtual particles are constantly be created and annihilated even in a complete vacuum, I like to know if there exist such a mechanism to spawn an anti-particle black hole can be any size not necessary stellar? I think black hole lose mass by gradually throwing out one of the pair of virtual particles before they could cancel out each other, so would this also apply to an anti-particle black hole as well if it does exists?


texts: How long was the hyper inflation phase? Haw can we know that it lasted for a period of time and not more or les time?


texts:
I'm having trouble understanding relative angular/tangential speeds at increasing altitudes above Earth's surface. In particular, I find this comparison of tangential velocities on Wikipedia very confusing. According to it, the tangential speed of Earth's surface (465.1 m/s) is different from the tangential speed required to "orbit" at Earth's surface (7.9 km/s). Why are these different values? My understanding of the Earth was always that material on and within the Earth is orbiting the center of the Earth just like satellties do. Time for multiple questions in one post...

Is material on Earth's surface not in free fall around Earth's center?
How are geostationary orbits even a thing? Seems like the only orbit that could be geostationary would be standing on the Earth's surface.
What changes as you orbit further above the Earth's surface? Does your angular speed increase or decrease? Does your tangential speed increase or decrease?
Is magma near the center of the Earth not rotating faster than material in the crust, like in an accretion disk?
Can two objects be orbiting (circularly) at the same altitude but with different tangential speeds?

Thanks in advance!


texts:
I understand that the Trojan points are located 60 degrees ahead and behind a planet in its orbit.  However, since there are quite a number of Trojans in Jupiter's orbit, they cannot all be exactly at that point. Presumably they orbit around it.
So what sort of orbits do they have? Are they circular or anywhere near so, or are they elongated along the orbit of Jupiter? If the latter how far can they get from the 60 degree point?


texts: Why do post main sequence stars enter the red giants branch?

texts:
I am an early graduate student in astronomy and have hard time understanding why do post-MS stars move up the RGB.

Here is what I understand about post main sequence evolution of stars. As their hydrogen core is exhausted, the core shrinks under its own gravity. This lets a region of previously too cold hydrogen enter hotter regions, thus starting a hydrogen shell burning process. While this process can keep the luminosity constant, it expands the envelope, hence lowering the temperature and moving the star to the right in the HR diagram.

Then suddenly, the star starts moving up on the RGB: slight or no temperature change, but sudden increase in luminosity. What makes the star move up the HR diagram all of the sudden? This is before the helium flash when the core starts burning helium.

Thank you!


texts:
This answer to How will microshutter arrays be used in the James Webb and future space telescopes? explains how multiple objects can be selected so that the throughput of a spectrometer can be enhanced (with some compromises somewhere) by recording spectra of more than one object at a time. The answer is worth a read if you haven't read it yet.
Another technique to get multiple spectra from a single telescope is to place (and sometimes articulate) high quality optical fibers at may locations at the focal plane. These days the number of fibers and objects can number in the thousands, so the output of several fibers can be lined up along the slit one spectrometer, and multiple spectrometers can also be used.
But here I'd like to look back in time to understand the beginnings of this technology.
Question: How were "microshutters" or other multiplexed or multi-object techniques first used in Astronomical spectroscopy?


texts: Finding angle between a given sky position and ecliptic pole

texts: Given a right ascension in degrees and declination in degrees (say, 88 degrees RA, -63 degrees DEC) I want to find the angle between that location and the ecliptic pole (90 degrees RA, -66 degrees DEC... are these the right values? What are the decimals following the 66? Most of my values that I'm working with are similar to the one I give, so which ecliptic pole, if any, does this correspond to?) How would I find this angle, I need a convenient formula (such as a dot product to find this angle). Thank you!


texts: Are black holes solely responsible for hyper velocity stars?

texts: I read that the stars orbiting around Sagittarius A* (a.k.a the supermassive black hole located at the heart of the Milky Way) move very fast (many times faster than our Sun moves across the galaxy), and it is believed they have enough speed to wander off. My question is, is any exception to this rule, where somehow some stars may break a stellar speed limit not due to a black hole in their vicinity?


texts: Could it have been possible for the Moon to be split without any observable effect on Earth?

texts:
Before asking my question, I'd like to clarify why I'm asking about something so absurd. A supersitious claim has been bought to me that in the past, the moon was split and seperated as a sign. My attempts at dissuading them by pointing out that half of the planet failed to observe it has been met with the reply that this is because it took place for a short period of time. After which ofcourse the moon was returned to it's original form, leaving no evidence :)
I would like to know if there would've been any effect observable on Earth resulting from such a massive body being split in two. Perhaps something to do with the effect of the sudden change in the Moon's gravity on earth? Or perhaps some other factor that would make such an act impossible?


texts: How long do solar eclipses last on Metis?

texts:
How long does Jupiter obscure the sun, from the perspective of Metis, the innermost moon of Jupiter?

In other words, how long does Metis remain in the shadow of Jupiter?

If it varies by time of year, what are the minimum/maximum values?


texts: Matter/mass exist into the space. Where does space exist?

texts: It is said that before big bang there was nothing. Not even space/time. So, now where does space exists?


texts: How feasible would it be to get to a planet orbiting directly opposite Earth?

texts:
Imagine that in addition to Earth, there was a second planet, say of one Earth mass, orbiting the sun - but on the opposite side of the Sun, and at the same orbital radius.

My question is - given today's technology, would it be feasible to try to launch something to reach that planet? A rover, a capsule, or something of the sort is what I have in mind.

There are a couple reasons I initially don't see a solution. First off, the escape velocity of the Earth is about 11.2 km/s. The Earth's orbital velocity around the sun is nearly 30 km/s. This means that if I were to launch a rocket in the opposite direction of Earth's orbit to reach this "second Earth", not only would I have to counter this 30 km/s orbital velocity, but I would have to provide enough thrust for double this velocity in order to maintain a stable orbit around the Sun at the radius that Earth orbits at - but in the opposite direction. I'm not quite sure if rockets can get up to velocities that high - I know that the Juno probe is moving at around 73 km/s, but I believe that was after a series of maneuvers involving a gravitational slingshot.

Perhaps there is another solution? One that popped into my head was to launch it at an angle to the plane of Earth's orbit, but I don't quite know how that would work out, given that unless some serious trajectory corrections were made, the rocket would not arrive anywhere close to the planet - as the planet would have moved in the time the journey took.

Maybe it involves taking a path that is closer to the Sun, and more elliptical? At this point I'm just throwing out everything that comes into my head.

Basically, I'm looking for some sort of general explanation here, with a rough idea that I could build on. And if it isn't possible with today's technology, what do we lack?


texts: How to determine scalar-to-tensor ratio r from CMB polarization spectrum?

texts:
CMB polarization spectrum can tell us about the primordial scalar and tensor perturbation. By analyze B and E mode angular spectrum power spectrum  and temperature power spectrum we can determine the scalar-to-tensor ratio r, as many articles implies.

I know that r is defined by the ration of amplitude of primordial tensor and scalar perturbation. But what we in fact measure is the power spectra. So I wonder how can we get the value of r from the spectra we measure thus we can study the physics of primordial perturbations and inflation.


texts:
The Earth's rotation is gradually slowing down. It was significantly shorter in the prehistoric past, but now we need to add a leap second every few years and we've not yet had to take any back. In fifty thousand years, it is thought we'd need a leap second every day.

The slowing down isn't constant, however. The earth speeds up occasionally and we don't need to add leap seconds quite so often.

When was the longest solar day on record?

I suspect the answer is sometime during the 1970s when leap seconds were a yearly occurrence. It is also possible I've made an error of understanding.

(If your answer is the Summer Solstice or the 25 hour DST day, that's not the type of day I'm asking about.)


texts: I read that Dragonfly44 is a galaxy mostly consists of dark matter, and it should contain a super massive black hole too. If there really is a dark SMBH, how does it lose mass? I think there is no way for dark matter to be converted into energy and vice versa, no?


texts: What is the probability that we are the first ever intelligent life in the whole universe?

texts:
What is the probability that we are the first ever intelligent life developed all over the universe?

Everything starts somewhere, Is there any probability that we are the beginners to be part of intelligent life all over universe?!


texts: What would happen to a neutrino that, traveling parallel to the black hole, crossed it's event horizon?  Would it come through the other side unaffected? Or, A neutrino and a black hole just happen to be traveling in the same direction but the neutrino get close enough to cross the event horizon.  Is it now trapped inside the event horizon even though technically it only interacted with the black hole on a gravitational level?


texts: How gently could a comet/asteroid/meteorite "hit" Earth?

texts: Could an object from outer space with the right velocity and orbit come into contact with the surface of our planet in a "slowish" manner?


texts: Is the earth bombarded equally in all directions by neutrinos?

texts: Perhaps it is hard to known for sure because neutrinos are very difficult to detect, although they do go through the earth in very large numbers. But are they passing through the earth equally from all directions or is it really depending on particular events in the universe. It's probable that the sun generates a lot of them, so perhaps in the daytime we receive more of them than at night. But besides the sun's radiation, are the neutrinos coming from everywhere? Or is it possible that the majority of them comes from one direction, and perhaps even has an influence on the earth's movement?


texts:
are all the planet in solar system the same plane in the space or not ? if yes is there any especial reason ? and if no how do they orbits then ?
as far as i know they are in the same plane , but is that mean they are exactly in same plane or its some thing near that ?
I would also like to know if they all orbit in the same direction ?
Is any of the picture below describing them true ?!


texts:
If Earth was a grain of sand in Buenos Aires

in what point in this observable universe map would be LA be?


texts: Is the effect when two planets passing each other different, when they pass in the same or opposite direction?

texts: So is the effect between the passing planets different whether they encounter in the same or opposite direction in their orbits with the same relative speed difference?


texts: What's the farthest object as determined only by parallax?

texts:
I'm wondering what the farthest object we know of, as measured only by parallax methods, from either earth or satellite based telescopes, and at either visible light or radio wavelengths.

Basically, if we had no other way of measuring distances,
 what would be the farthest object we knew about? I'm guessing this measurement would probably be one from Gaia, it being the latest telescope to measure such things TTBOMK.


texts: Properties of low-mass stellar remnants vs the Earth

texts:
How does the Earth differ from a (low-mass) stellar remnant, which has stopped fusion and the outer layers of which have been blown away?

Could a stellar remnant end up with a similar relative abundance of elements as the Earth?

i.e. Is it possible that a star loses so much matter when it dies that the remnant doesn't turn into degenerate forms of matter?


texts: Happy lunar new year! When will "sunset" happen for Chang'e-4 and Yutu-2?

texts:
Firecrackers all night and all libraries being closed here are two good indicators to a nerd like me that Lunar New Year has come again, and that means that it's the beginning of a lunar month and new Moon as seen from Earth.

That also means that the Chinese lander Chang'e-4 and rover Yutu-2 should be in sunlight since they are on the far side of the Moon.

What phases of the Moon as seen from Earth correspond to times of sunrise and sunset for those two?


texts:
As a general science (hence Wikipedia!) reader, the latest information I have is that 60 galaxies "have been found and counted" inside the Boötes void, this of 1997.

(1) What is the latest count of galaxies "known" inside the Boötes void?

The Boötes void is a ball 250 million light-years across. (Say, .002 of the width of the visible universe?)  It seems - unbelievable - it has only 60 galaxies.

The "60" value (or some new number since 1997), maybe I am misunderstanding it, or it is misreported, or has a different meaning?  Galaxies are counted in the thousands or tens of thousands, it seems hard to believe in a cosmological space, the number "60" would come up.

So, what is (2) the thinking on how many galaxies there likely are in the Boötes Void? An order of magnitude.  Is it "about 100," or "about a trillion," or what?

What do you (3) normally quote galaxy density in?  Galaxies per Gpc3, or?

Indeed, I am trying to get a (4) comparative sense of galactic density in the Boötes void versus elsewhere. What is the galaxy density in the Boötes void, versus the universe in general, or if it's more meaningful versus perhaps superclusters, walls, or?

Is it "one tenth as dense"?  One zillionth?  One half?  Just how void is that sucker?

Further...

BruceS below has usefully pointed out that, indeed, the "60" galaxies are anyway only in a small tube which apparently cuts through the Boötes Void.

Does this mean that, incredibly, the actual main body of the Boötes Void - putting aside that tube - is literally empty, no galaxies at all??

That seems totally incredible.  I feel we really need a galaxy-counting astronomer to clarify the nature of the Boötes Void.


texts: Does Ganymede have a day/night cycle? If so, what does it look like?

texts:
Over on the SF & Fantasy Stack, I've asked a question about a curious watch that shows 15 intervals on its watch face instead of the usual 12 hours. That watch belongs to someone living on Ganymede, close to the end of the 21st century.

Why does Jet's old watch show 15 hours?

Does Ganymede have any day/night cycle, or any other cycle, that would explain this curious watch?

In analogy to earth, we should expect a 30-hour Ganymede-day. But Ganymede is in tidal lock, always showing its same side to Jupiter. Also, calculations show that the light reflected by Jupiter pales compared to that of the sun.

So I would assume that Ganymede's day/night cycle is sun based, possibly complicated by passing through Jupiter's shadow.

What do day and night on Ganymede look like?


texts: What happens if I were to add angular momentum to a maximally spinning black hole?

texts: I am aware that a "naked singularity" is not possible. However, what would happen if I added angular momentum to a black hole near the maximal angular momentum limit? Does it asymptote?


texts: Delay between neutrino pulse and visible flash of supernova

texts: If you were orbiting a star undergoing a core-collapse supernova, what would be the delay between the neutrino pulse from the collapse and the first visible effects on the surface? Basically, I'm trying to get a scientifically-plausible gauge of the warning time given by said neutrino pulse.


texts: Did Arecibo's secondary optics compensate aberrations when viewing farther away from vertical?

texts:
In the beginning of the short YouTube video Arecibo Uncut: Under the Dish with Phil Perillat it is mentioned that while dish antennas are usually a parabola, the problem is that a static parabola would only be useful to see objects for a few minutes as they passed overhead.

But then some guy at DARPA says "Hey why don't you guys make it a sphere?" A sphere has the unique property that from the center of curvature, no matter where you look, it's the same.

That is indeed how the Arecibo dish works; a static primary sphere and a big, funny-looking secondary mirror and associated optics/electronics suspended above on cables that can be moved around in order to "point" in different directions.
Two questions:

While the statement in the block quote about the sphere is correct as far as it goes, was the shape of the correcting optics (secondary, etc) above also independent of where you look? Or ideally would you like a different secondary shape depending on how far off-vertical you look? If so, is this what happens?
Any ideas who "the guy at DARPA" might be?


texts: The Hubble telescope can see the light from the big bang.My question is if our universe is expanding that would make everything that's in front of our solar system be in the future? And also can Hubble see ahead of our solar system and does the bang big light ends behind our solar system?


texts: If the earth stopped rotating, would we really fly inertially at 1000mph?

texts:
I heard this on Prof. Neil Tyson's StarTalk podcast (this episode) and had a question about it. In a Q&A session, a listener had asked what would happen if Superman really did stop the earth from rotating and rotated it in the other direction. Prof. Tyson's response was that if the earth, which is rotating at approx. 1000mph about its axis, is stopped, everything that is not anchored on earth will move the opposite direction at 1000mph and we'd all go crashing into things at that speed.

I suppose that is just simple inertia: if a body moving at 1000mph is stopped abruptly, everything that was moving with it but not attached to it would indeed attempt to continue in the same direction at 1000mph. However, the earth is rotating rather than moving in a straight line. Essentially, gravity is strong enough to ensure that we are not thrown off into space by the centrifugal force from the earth's rotation (we aren't holding on to our dear lives as the earth turns at 1000mph). So in a sense, aren't we anchored to earth by gravity? And therefore, doesn't it mean that if the earth stopped abruptly, we'd just stop with it? (I'm thinking of say a centrifuge with test tubes attached to it. Though as I think about this, I feel that we'd sway at the point of attachment instead of stand still, were the earth to stop).

Can someone help resolve this for me?


texts: When stars explode why can we still see them?

texts: This might be a silly question but if light travels at the speed of light and time is frozen in that speed then why the stars we see could be dead already and not just instantly disappearing from the sky the moment it explodes/dies?


texts: Blinking Star-Like object in the sky? What could it be?

texts:
I was out camping with my family at Crater Lake in Oregon. And I was looking up at the stars for a little while when I noticed a star-like object blink, then disappear. I thought I might have been going crazy for a second because I was watching the sky for a while, but then I noticed it blink again but in a different spot, further down. I was watching for a bit and a few seconds later, it let off another bright blink for about a second in a different spot again, and then disappeared.

It did this for about a solid 5 minutes before completely vanishing and never blinking again in the middle of the sky. I realised this blinking was going in a downward zig-zag pattern, there was no way it was a plane, and no way it was a satellite. I showed my family and they saw it too when it was happening, so it wasn't just me.

The object was almost exactly the same brightness as all the other stars but maybe a bit more bright. I have no idea what to think of this, and the object was as big as all the other stars too, I found it weird though that it lit up, then disappeared for a few seconds to just reappear in a different spot kinda far away over and over again.


texts:
On the TRAPPIST telescope, the filter wheels are described to have a filter with the following description:

  NIR Luminance I+z' (>700nm)

After a bit of googling, I wasn't able to find what the specifics of this filter are (its FWHM and mean wavelength).

How would I go about finding these qualities of this filter?


texts: Star formation: When a nebula collapses, is it only the gasses that form the star?

texts:
A nebula is made of dust (elements heavier than He and H) and gas (H and He).

Stars are made when nebulae's collapse and hydrogen begins to fuse. 99% of nebula material goes into making the star. The left-over 0.01 of debris creates planets.

Does 99% of nebula material that makes the star only consist of gas (He/H) and the 0.01% is the dust which makes the planets?

Question Clarification:

Are the constituents of the 99% of mass that makes the star and the 0.01% mass that makes the planets the same?

I.e.

Does both the 99% and 0.01% compose of mainly He/H and a small portion of metals (meaning the star contains heavier elements like Si and Fe etc before fusion?)
OR
is 99% of the nebula composed of He/H, which collapses to form the star, and 0.01% consists of heavier elements that make the planets?


texts: I understand what black holes are, and how they form, but I was recently introduced to the topic of detached black holes. What are they and how are they different from standard black holes?


texts: I recently saw the first image of a black hole. As I understood, it is covered with bright, hot matter. In this case, how can we see the black disk (event horizon), instead of a bright disk due to the matter surrounding the black hole? Or is the matter around the black hole disposed in a disk shape and the astronomers got lucky that the disk was not oriented towards Earth?


texts: Where is the intervening light in the M87 black hole?

texts:
The M87 black hole is at the centre, more or less, of an elliptical galaxy of 1 trillion or more stars. So certainly there are stars and other light emitting objects (emission nebula e.g.) in the intervening 53 million light years between earth and the black hole.

How is it that the centre of the black hole image is perfectly dark, as if it is being observed directly, with not one point of light between the black hole and earth? I appreciate that space is mostly empty, but do we really have an unobscured line of sight to a black hole in the centre of an enormous elliptical galaxy?

Does it have something to do with the type of light being observed?


texts: Do neutrinos have as much information as photons do?

texts:
If neutrino detectors keep improving so that a fair number of neutrinos can be observed, would they be as informative for astronomy as photons are?

They are of course a very valuable complement to photons, but I'm thinking about neutrinos in and of themselves. Photons have wavelength, spectral lines, redshift, diffraction, polarization which reveal their origin and interactions on the way to us. Do neutrinos say more than just what direction they come from?


texts: Can there be elliptical rings around a planet?

texts: The rings of Saturn and Jupiter are circular. Orbits can be elliptical, so can rings be elliptical?


texts: Bright light in the sky, in the '90s, what could it have been?

texts:
Sometime in the summer months during the years from 1993 to 1998, my friend and I saw what looked like a gamma-ray burst (or what looked like an artist's impression of it). It looked like a star that got very bright (within a few seconds) and we saw what looked like a line shooting out from the sides of it that spread across our field of vision. All this happened in less than 10 seconds.

I can't confirm when it was any more exactly than that, unfortunately, as we were walking near my friends house at night in the summer, as we did hundreds of times in those years.

According to Wikipedia, the first naked-eye brightness gamma ray burst happened in 2008, so I imagine that's not it.

What could it have been?


texts: Is there an upper limit to the mass of terrestrial planets?

texts:
The exoplanet Kepler-10c has a mass between 15 and 19 times the mass of the Earth (making it comparable in mass to Neptune), and yet is thought to have a density of about 7g/cm3 and to be a terrestrial planet, with a substantial proportion of "hot ice"

Is there an upper limit to the mass of terrestrial planets, or can rocky planets form that are larger than Kepler-10c?

This, older, article in Universe Today suggests that terrestrial planets can't form more than 5-10 Earth Masses, substantially smaller than Kepler 10c.


texts: What is the light that we see from a neutron star come from?

texts:
What hold the electrons in orbit? Is it gravity or the atomic attraction between the protons and neutrons?

I asked this question on Physics SE I hope I improved on the quality enough to do better here.

Is the light we see from a neutron star from the neutrons or the electrons?


texts: What wavelength to best detect the "9th planet"?

texts: We know that the reflected sunlight will make detecting the 9th planet very difficult in the visible light. Is there another band that will be more likely to detect it? What is the surface temperature of this object likely to be, and what would that mean about its optimal detection wavelength?


texts: Exoplanet dip in transit light curve when the planet passes behind the star

texts:
In the animation below, I don't understand why the brightness slightly decreases when the planet is behind the star.

Where does this effect come from?


texts: I am looking for basic data regarding red-shifting that  comes with reliable measure of distance of the emitting star.


texts: Can we, with arbitrary precision, calculate what's the place on earth that's closest to the sun on a given day?

texts: Can we, with arbitrary precision, calculate what's the place on earth that's closest to the sun on a given date? If so, what's the math like? Say, if I wanted to calculate this within 1m, 10cm or 1cm precision, what exactly should I take into account?


texts: What (the heck) is a Super Worm Equinox Moon?

texts:
Google News feed shows me the following.

What does the term "Super Worm Equinox Moon" mean and has it ever been used before this 2019 clickbait instance?


texts: Why does squinting make hard-to-see objects clearer?

texts: So I, like most other astronomy enthusiasts, have, at some point, not been able to see something clearly, such as a star, and have had to squint to be able to see it better. When this happens, the object seems to become clearer, but the light seems to gain a cross, or sometimes a hexagon, or an irregular line shape when doing so. I've noticed a similar effect on different models of telescopes, especially the newtonian reflector series. More on this here: (http://www.youtube.com/watch?v=ipe3NN1yPzM). Is this a similar effect on the eye? But more importantly how does squinting improve the quality of the picture?


texts: Will all of the gas in the universe be converted into red dwarf stars?

texts:
Red dwarfs have lifespans of trillions of years and are also the most abundant stars, making up 70% of the stars in the Milky Way. No red dwarf star has ever died and none will die for a very, very long time. Because it take so long for them to die, they're not releasing their hydrogen back into the interstellar medium to make new stars.

As more massive stars live and die over the course of years, those stars release their hydrogen into the interstellar medium, which can form new stars, 70% of which will be red dwarfs. Does this mean that, billions of years into the future, all of the matter will get locked within red dwarfs until they begin dying out trillions of years later?


texts: Relationship between IMF and time spent during an evolutionary phase

texts:
I was reading a little about stellar evolution and was wondering whether there was any relationship between the lifetime of an evolutionary phase and the IMF, I searched on google but all I found were claims that there is a relationship, but I couldn't find any numerical formula which explains this. Does there exist such a formula that relates the lifetime of an evolutionary phase with the IMF and other properties?

For example, given the luminosities, IMF, number of stars, can we determine the lifetime in,say the RGB or the subgiant branch?

I know that main sequence lifetime is proportional to $M/L$, was hoping to get such a relation for other branches


texts: Was that actually a shooting star during the supermoon eclipse on September 27th 2015?

texts:
During the super-moon total lunar eclipse on September 27th a meteor-like streak passed very close within view of the event. It appeared to happen at the very middle, the maximum eclipse.

[CafferyPhoto][1]

At the time, I thought it must have been some organization shedding an unused satellite. This would be a pretty epic time to do so as so many eyes around the world are looking at the same thing. Maybe even NASA marking the halftime of the event. Can anyone confirm or shed any amount of light on what this was?

[1][https://www.facebook.com/cafferyphoto/photos/a.279223605465113.81307.120967987957343/915070541880413/?type=3&theater]
note - photo for proof only - shutter cut off leading edge

QUESTIONS:

People on the Caffery's Facebook page seem to have seen in in California and other locations as well, I happened to be in St Thomas, Virgin Island at the time of the event.  CafferyPhoto quotes. "I was only exposing for half a second so the shutter cut off the latter half of the trail, darn it!" - Seems in was taken in the NorthWestern US sometime around 7:30pm.


texts: Near-future astronomic events that could threaten Earth

texts:
What kinds of astronomical events can pose a serious threat to life on Earth in the near future (1000-10,000 years). If there are none in the near future, when is the soonest event that is predicted to threaten life on Earth?

I am ignorant about astrononomy and so far I have only thought of an asteroid collision, solar flares, and effects from the sun dying in several billion years (and a visit by some hostile aliens).


texts: Ternary (or trinary) stars are not the same as triple stars. So, what is the basic underlying difference between these two? What are some popular examples of these two varieties?


texts: What do we know about the lifecycle of the Milky Way (or any other spiral galaxy)?

texts:
I know that the Milky Way will collide with Andromeda in the distant future but my knowledge about the lifecycle of a galaxy is very lacking.

I was surprised that Wikipedia is so sparse on information in this topic. So how can I visualize its lifecycle? What will happen in the future?

FYI: I just found this very informative video on the topic.


texts:
I am pretty new to astronomy, and I have fallen down rabbit hole creating a new Metonic calendar in Javascript.

As part of this I would like to calculate when the sun is half way between a solstice and an equinox as viewed on a horison. Forgive me if my terminology is off but I believe this is known as the azimuth.

My issue is that I do not know what the correct values are. I am already  calculating the solstice and equinoxes using the suncalc javascript library

https://github.com/mourner/suncalc

in this code are the following 4 lines that determine the solstices and equinoxes. 0 is the spring equinox and 3 is the winter solstice.

switch( k ) {
     case 0: JDE0 = 2451623.80984 + 365242.37404*Y + 0.05169*POW2(Y) - 0.00411*POW3(Y) - 0.00057*POW4(Y); break;
     case 1: JDE0 = 2451716.56767 + 365241.62603*Y + 0.00325*POW2(Y) + 0.00888*POW3(Y) - 0.00030*POW4(Y); break;
     case 2: JDE0 = 2451810.21715 + 365242.01767*Y - 0.11575*POW2(Y) + 0.00337*POW3(Y) + 0.00078*POW4(Y); break;
     case 3: JDE0 = 2451900.05952 + 365242.74049*Y - 0.06223*POW2(Y) - 0.00823*POW3(Y) + 0.00032*POW4(Y); break;
   }

can anyone help me understand what the values might be to determine the halfway points between these solstice and equinox values?

thank you for your help.


texts: What's the furthest object observable by the naked eye from earth?

texts:
From XKCD:

Caption: 'The light from those millions of stars you see is probably many thousands of years old' is a rare example of laypeople substantially OVERestimating astronomical numbers.

So, what is the furthest object visible to the naked eye in the night sky from the surface of the earth? Assume a person with good eyes, on a clear, dry night at sea level, away from bright lights.


texts: What gases do you need to start the creation of a star, and why do you need these gases? What are their functions?


texts: Combining lenses from two telescopes to build a more powerful one?

texts: I have two Galileo 700mm x 60mm Astro/Terrestrial Refractor Telescopes. Can I take the lenses out and make one powerful telescope, something like an optical series circuit?


texts: How big and how far away would the moon be if earth was the size of Jupiter?

texts: If the earth were the size of Jupiter, what would its 'moon' be in both relative size and distance? I did some quick figuring and think I roughly figured out that if placed at the position of the sun, Jupiter's moon would be Neptune in both relative size and current distance from the sun. That seems very distant and I'm questioning my calculations. The moon is 27% as large as the earth and is ~27,700 times the earth's diameter distant. Jupiter is ~87,000 miles in diameter. That would make it's moon ~23,500 miles in diameter and ~2.41 billion miles distant. Neptune comes relatively close to those results. It would be slightly larger than our moon (30,600 miles in diameter vs. 23,500) and slightly farther away (2.8 billion miles away vs 2.41) but still close for comparison purposes.  That puts the moon relatively MUCH more distant from the earth than what I would have thought off the top of my head.


texts: How are constraints on dark energy improved the most?

texts:
Today we have various data available from independent probes to constrain dark energy, i.e. its equation of state $w$. These include Type 1a supernovae, BAO, CMB, large-scale galaxy surveys, etc. Are any of these probes better/more powerful at constraining dark energy than the others? Why or why not?

For example, I assume that if a galaxy survey includes 1000 galaxies in a redshift range $0.1<z<1.2$, that would result in higher constraints on $w$ than just using 500 Type 1a supernovae in a range $0.1<z<0.8$. But how much of a difference does this, among other factors I'm unaware of, make? Quantitatively, how do the errors/uncertainties scale with larger samples and larger redshift intervals (I think for a larger sample the uncertainty decreases as $1/\sqrt N$)?

It also makes sense that dark energy models with more free parameters would come with a larger uncertainity (for example, $wCDM$ has 1 more free parameter, $w$, than $\Lambda CDM$). But how much is the constraining power diminished for each new degree of freedom? See plots (Figure 9, https://arxiv.org/pdf/1709.01091.pdf):

In the plot on the right, clearly the constraints are much looser because more free parameters were introduced in fitting the data to this time-dependent dark energy model. We can also see that the SN1a data, for example, seems to constrain dark energy less than CMB or BAO data. Why is this? Is it because SN1a have only been observable at lower redshifts so far?


texts: How much more mass would Mars need to currently have enough pressure for liquid water and oxygen?

texts:
My question is whether Mars just about failed to meet the threshold or missed it by a lot. It's been dry for 3 billion years. How much bigger would it have needed to be to buy it that extra time? Let's say in modern times we turn up and find it has enough CO2 to be as warm as Earth, and has small seas in the lowest lying regions north of the equator.

Based on this chart (I found in a Google image search) it seems that Mars should be about twice as massive to avoid water vapor reaching escape velocity. If Mars is twice the mass then for the same density (although actually it would automatically be more due to being squished by its own mass) it should have an escape velocity of around 6.324km/s. If it had the same density as Earth due to an iron core (though again Earth gets extra density from squishing its core), then the escape velocity should be 6.69km/s. A double massed Mars should probably have an escape velocity somewhere between these two extremes. 6km/s seems to be the threshold for maintaining water vapor at current Martian temperature, though the issue is that having a thicker atmosphere would warm Mars up a lot. If it had enough greenhouse gases to be the average temperature of the Earth at its current semi-major axis then perhaps the escape velocity needed would be more like 7km/s, which could mean a Mars around 3 times the mass (depending on how much we fiddle with the density). I can't factor in the effect of a strong magnetic field.
Is my quick estimate overzealous? Am I missing anything?


texts:
I'm trying to calculate the state of the Earth at a given time using Keplerian orbital elements from this page. It has the following instruction:

  Compute the coordinates, $\mathbf r_{ecl}$, in the J2000 ecliptic plane, with the x-axis aligned toward the equinox:

So after this calculation we are supposed to know direction of some equinox. But there exists the phenomenon of precession of equinoxes, so this direction shouldn't in general be fixed. I assume the equinox mentioned in that document is some "mean" equinox for the range of dates the data are valid for.

So, how do I calculate the true equinox position/direction, given these data?


texts: If we accelerate a neutron star to move at speeds comparable to light would it become a blackhole because of the added energy?

texts: Could a neutron star turn into a blackhole if it is accelerated to near luminal velocities? And if it slows down after a while, does it become a neutron star again?


texts: A paper appeared at the arXiv.org (in April or May) claimed that the writers have found the gamma rays emitted by annihilation of dark matter in a satellite galaxy of the Milky Way by examining the Fermi data.  I cannot find this article anymore.  (It is possible that the writers withdrew the article.) Has someone actually detected gamma rays emitted by neutralino (or any other dark matter) annihilation?


texts: Can we know the orbital planes of extraterrestrial planetary bodies?

texts:
Astronomers can tell if there are any exoplanets orbiting its parent star using but not limited to the following methods:

Transit

As an massive object usually a planet passing in front of a star causing the amount of light emitted from the star to dim, by measuring the dimness the data can reveal how big the planet is.

Radial velocity

The star will seems to wobble as if there is a massive object usually a planet in orbit playing tug of war in a game of whose gravity is mightier. However since this wobbling effect is difficult to observe nerds prefer to measure the blueshift of the light (as star accelerates in our direction) and redshift (as star accelerates away from our direction) which seems to also tells how massive the planet is.

Note
Astronomers can derive the planet's density from its mass and radius(see transit).

Question

So far astronomers are able to determine the size, mass as well as density thus even its composition, is there any way to find the angle of the orbital plane of the exoplanet orbiting its parent star?


texts: Do bigger telescopes equal better results?

texts:
There are many large reflecting/optical telescopes around the world, just to name a few: the Very Large Telescope, Large Zenith Telescope, and European Extremely Large Telescope.

My question is does actually building larger telescopes improve visibility of the universe, quality of an image, and various other attributes of a telescope?

Well it does seem kind of obvious that a larger telescope may have more magnification and better imaging, however if that is true than why don't we just build a super large one (think really really big, unlike the size of the current large ones) so we can see the universe in HD - so to speak?

Since we haven't done this yet (I think) is it because of financial issues or is it because simply building a bigger telescope won't improve much to visibility and image quality?


texts: How can one determine the angle between the line of nodes and the major axis of the orbit of Mars?

texts:
Edit:

What I really was looking for, was the difference in longitude on the orbit of Mars between its aphelion and the point where the north pole axis of Mars would point towards the Sun (northern summer sostice).
I found out with this article of the Planetary Society that the solar longitude (Ls) is 90⁰ for northern summer solstice and Mars is at aphelion at Ls = 70⁰.

I know when northern summer is on Mars, the solar radiation on its surface has a minimum of 492 W/m², meaning that is also the time when Mars is furthest from the Sun.
So this would coincidence somewhat with the north pole of Mars pointing towards the Sun.
But what is exactly the angle between the line  of nodes and the major axis of its orbit ?


texts: Does a 4-manifold universe imply zero net energy?

texts:
If our universe is a 4-manifold (i.e. with every point in space-time already existing) does this imply that there is zero net energy (as net energy would do work and so change the universe)?

If so, how do we account for the fact that our current experience of the universe is very far from net zero energy? Are there stores of negative energy out there? (Or, more likely, have I misunderstood this question?!)


texts:
I've been reading some of Stephen Hawking's work on the theory of the expansion (and ultimate contraction) of the universe and was curious if anyone has every hypothesized that the universe has possibly gone through this cycle before (or many many times before).

I know it would be impossible to determine because the idea of the universe contracting back to the size it was at the point of the Big Bang (or at the end of a Big Crunch) suggests that all of the laws of physics would break down but has anyone hypothesized and written work on this. I'd be curious to read more about the idea if so.


texts: Binaries consisting of a black hole and a non-black hole?

texts:
Are there any known binary systems in which one member is a black hole and the other is not a black hole (main sequence star, giant, neutron star, white dwarf, whatever)?

Googling seems to turn up only discussion of binaries in which both components are black holes. Is there some astrophysical reason why the kind of system I'm talking about cannot form? I think I remember that gravitational wave observatories have talked about black hole-neutron star mergers, but are such systems purely hypothetical so far?

I guess Sagittarius A* is sort of close to being an example, if you count it and the stars orbiting it (or orbiting their common barycenter) as a multiple star system.


texts: Would a killer asteroid shattered into thousands of pieces produce the same devastation?

texts:
If we blow up a global killer (in the 3 - 20km range) days before impact into enough pieces that none of the them exceeds, let's say, a 30m diameter and the impact pattern is dispersed over most of the athmosphere, would that be a possibility that the impact energy is soaked up with less catastrophic consequences than the hit of the asteroid in one piece? Or would the distributed energy heat up the athmosphere so much that it would kill higher life instantly or eventually over chemical/biological chain reactions?
Or would the early impacts heat up or disturb the athmosphere so much that later (in the range of seconds or minutes) impacts would experience not enough friction so that there would be a surface bombardement with millions of little pieces?


texts: Stars moving in a straight line in Minnesota

texts: I was outside at around 7:50 to 8:09 ish. At I looked up in the sky to see around 20-50 stars or something moving in a straight line at the same speed. I have never seen anything like this ever. And they keep appearing out of nowhere. Felt like I was at a firework show except no explosions and cool lights. Kinda freaky if you ask me


texts: Can a habitable planet be smaller than 0.58 Earth radii?

texts:
According to the below image, the lowest escape velocity a planet can have in order to still be able to retain water on its surface and have a temperature above freezing is 6.5 km/s minimum.
With Earth density (which is already a pretty high density to have for a planet smaller than Earth), 0.58 Earth radii has an escape velocity of 6.488 km/s, 0.585 Earth radii has an escape velocity of 6.544 km/s, and 0.59 Earth radii has an escape velocity of 6.6 km/s.
More narrowly, 0.581 Earth radii has an escape velocity of 6.499 km/s, while 0.582 Earth radii has an escape velocity of 6.51 km/s.  Thus, hypothetically, the smallest habitable planet has between 0.581 and 0.582 Earth radii.
My question is, is this true?  Is it impossible for a planet smaller than ~0.58 Earth radii to maintain liquid water on its surface?
This chart implies that a planet smaller than this can only retain water on its surface in its frozen state, or otherwise a lower escape velocity even if the planet were in the habitable zone would cause the planet to lose its water over cosmological timescales.
The only alternative would be to have a higher density than Earth which would increase its mass, gravity, and escape velocity, but as I said, Earth density is already quite high for such a small planet.

(source)


texts: Is a spotting scope or binoculars a better choice for astronomy?

texts:
I'm interested in observing the moon and planets, and maybe some nebulae and star clusters.

I have a pair of binoculars:

Nikon OceanPro 7x50 binoculars (around \$300)
Celestron 20x80 binoculars (around $100)

I'm looking at a step up, to 100mm. Specifically, I'm trying to choose between  25x100 binoculars (either a Celestron or an Orion) and a 100mm spotting scope.

The only reason I'm considering a spotting scope is that it has a magnification of 22-66x, compared to the binoculars' 25x. But I want to check if such high magnifications really work for astronomy.

Let's say I'm observing the full moon. What's the highest usable magnification, without resulting in too dim an image?

An Amazon review says that:

  I have found that while the readability improves from 22x to about 38x
  the resolution actually decreases after that and I never use it from
  40-66x, there is no point. Maybe it would have been better to have
  optimised it for 22-40x.

If the scope is limited to 40x in daytime use, I expect it to be worse at night, even observing the full moon.

I'm considering buying the scope only for the increased magnification over the binoculars, but if I end up using the scope only at 22x, it defeats the point of buying the scope in the first place. Should I stick with the binoculars?


texts: Search satellite locations on the sky by date and coordinates

texts: I would like to know what satellites, asteroids, comets, etc passed through a certain coordinate or region on the sky at a certain date. I have found sites like NASA's HORIZONS, but this searches for coordinates for a specific object only. Does a tool to perform this type of generalized search exist?


texts: What would happen to a gas planet if its core mass goes beyond the Chandrasekhar limit?

texts:
Hypothetically, let's say we had a gas giant that continued to accrete mass. I've heard that the cores of gas giants are electron degenerate. So if the planet continued to accrete mass and the core mass went beyond the Chandrasekhar limit, what would happen?

In white dwarfs, the result is dependent on the composition. Carbon-oxygen white dwarfs will undergo carbon fusion, leading to a type 1a supernova. Oxygen-magnesium-neon white dwarfs will undergo rapid oxygen fusion, leading to a rapid ignition and supernova but leaving behind a neutron degenerate core.

So would the composition of a gas giant's core play a similar role, if it went beyond the Chandrasekhar limit? What would happen if, say, Jupiter somehow accreted a core mass beyond the limit?


texts: Conversion of UBVRIJHK magnitudes to luminosity?

texts:
So, I know that the standard for conversion from bolometric magnitude to luminosity established in 2015 equates to:

L = 10^(-0.4 * magnitude) * 3.0128e28

Easy enough. But what does one do about luminosities in specific bands? I've seen some information that makes it look like it should be something like:

U: 10^(0.4*(5.61 - U-band magnitude)) * 3.828e26
B: 10^(0.4*(5.48 - B-band magnitude)) * 3.828e26
V: 10^(0.4*(4.83 - V-band magnitude)) * 3.828e26
R: 10^(0.4*(4.42 - R-band magnitude)) * 3.828e26
I: 10^(0.4*(4.08 - I-band magnitude)) * 3.828e26
J: 10^(0.4*(3.64 - J-band magnitude)) * 3.828e26
H: 10^(0.4*(3.32 - H-band magnitude)) * 3.828e26
K: 10^(0.4*(3.28 - K-band magnitude)) * 3.828e26

But I'm not sure about these, because I've seen varying figures from varying sources for the magnitude of the sun in various bands.  I'm trying to extract the luminosity values from PARSEC data.

Speaking of PARSEC data, the documentation is rather lacking, so any clue about the following fields?

McoreTP: Sounds like it should be something about core temperature, but the value is usually either 0, or something small like "0.546"

Mloss: Presumably mass loss, but there's no units!  But I can probably work out the units just by comparing how star masses change over time....

Tau1m: ??? Usually 0.00, but sometimes something small like "0.06"

Cexcess: ??? Generally "-1.000", but sometimes things like "7.356".  Note that there's an entirely separate field for Xc, which is clearly carbon mass fraction.


texts: Are these parallel lines I'm seeing in this image a real pattern on the Moon?

texts:
In this question I mention the GIF in EarthSky.org's Moon Phases update Lengths of lunar months in 2017. After watching it a while, I've noticed a pattern of parallel nearly vertical lines on the Moon image that's used to generate this simulation. I've shown it below. However, if I look at the moon image in Wikipedia, which is much larger, higher resolution, and has perhaps higher contrast, I don't see it.

It could be there, but less noticable due to the enhanced level of detail i the large image, but I am wondering - is it real, or not. If not, how did it get into this image?

above: Animation used in EarthSky.org.

above: Frame 29 from the GIF Animation used in EarthSky.org.

above: A casual analysis of the cropped ROI. The traces are color: top, middle, and bottom third, column averages, black: entire column average. Short vertical lines are drawn by hand to try to point out the pattern that I'm seeing.

above: "Full Moon photograph taken 10-22-2010 from Madison, Alabama, USA. Photographed with a Celestron 9.25 Schmidt-Cassegrain telescope..." from here.


texts: Landing on an "earth-like" planet (practical application)

texts:
This may not belong here in astronomy and my apologies if that's the case.
The hypothetical:
We find, and are able to travel to (in a reasonably short amount of time), a planet that is for all intents and purposes a second earth: it has close to the same atmosphere, gravitational force, a stable orbit, land and liquid water, preferable temperatures, vegetation and other life , etc...

From a 'War of the Worlds' approach to this, wouldn't it stand to reason that we still would not be able to land on the planet and exit our spacecraft without suits to protect us because of the fundamental aspect of our immune systems? That is, our bodies have adapted and continue to adapt to Earth's lifeforms but have absolutely no tolerance to another planet of almost identical properties and therefore would perish shortly after exposure, yes? So I wonder, does anyone know if there is a plan for the hypothetical scenario to gradually expose individuals to the new environment and if so, what is the plan? For example, we could try to collect at least some of the potentially hazardous bacteria and viruses for vaccination? (maybe, not sure how that works even on Earth)


texts: Moon's and nodes' inclination to the Invariable plane

texts:
Moon is inclined to the ecliptic 5.14 degrees. Earth's inclination to the invariable plane is 1.57869 degrees.
What is the Moon's, and node's inclination to the invariable plane?
Since the Moon has an inclination to the invariable plane, that means at any point in time the degree of inclination is different depending on the Earth's position. where can I get this information of planets' inclination degree at any date? Calculated by NASA JPL Horizon?


texts: How did scientists come to the conclusion that it is space that is expanding?

texts: How did scientists come to the conclusion that it is space that is expanding and not galaxies moving away from each other as in a giant explosion?


texts:
In Wikipedia they write that Eris has an atmosphere when around perihelion (close to the Sun) which collapses when Eris moves away from the Sun. So it behaves similar to a comet's tail. However, they thought the same of Pluto's atmosphere, and the information on Wikipedia is from prior to the New Horizons Pluto flyby which proved that Pluto has a permanent atmosphere.

Could they be wrong on Eris too or does Eris really go far enough from the Sun so that its atmosphere collapses? It is possible that they are right with Eris for its aphelion is about twice as far as Pluto's, but are we sure about its atmosphere?


texts: How small can a planet be and still have Earth-like gravity?

texts:
A planet made from denser material than Earth might have equal gravity to Earth but a smaller radius. How small can a planet be and still have Earth gravity?

Ideally it should be habitable by humans, so not made of anything dangerous, radioactive or unstable.


texts: What area of Proxima Centauri would need to be occluded for the effect to be observable on Earth?

texts:
One of ideas of how Breakthrough Starshot could communicate data from Proxima Centauri is to have a massive swarm of the solar sail powered craft to pivot (with their sails) synchronously, taking either 'sideways' or 'head on' orientation to the star - in effect either obstructing it or revealing for an observer 'behind' - on Earth. If the swarm is big enough, it would cause an observable dimming of the star - and timing the pivots right it could encode data in the star's visible luminosity.

The primary question of viability of this idea lies in 'how big a swarm?'. What percentage, or what absolute area or a star like Proxima would need to be occluded for the effect to be observable? We can notice transition of exoplanets quite reliably so that would be the upper bound, but what's the smallest object area that would make a detectable difference?


texts: Does the light from a torch reach to the moon?

texts: If a torch is switched on and pointed towards the moon, would the light from the torch reach to the moon?


texts: Material exchange between a planet and its host

texts:
Of the exoplanets found so far, is there one that can exchange material with its host? How could we prove that?

Io might be a good example, but it is not a planet.


texts: Are multiple geostationary satellites required to handle arbitrary locations?

texts:
Do geostationary satellites need to have the equator as the plane of rotation, and the earth's centre to be the centre of rotation? Can it rotate over, say, the Tropic of Cancer, focusing on a single city?

If not, in which case, we need a chain of geostationary satellites to do a function, why employ geostat satellites at all? Aren't there satellites at lower altitudes which could do a better job?


texts: How much does subatomic particles such as photons, tachyons, and electron being the biggest particles etc. occupy space? If put in a ball how big of a ball would that be?


texts: 2 Earth-like planets in co-orbital configuration

texts:
I am trying to set up 2 Planets in a co-orbital configuration around a Jupiter size planet similarly to Saturn's moons Janus and Epimetheus. I'm trying to do this in Universe Sandbox 2 but when I place these planets they mess with each others orbits too much. Is it possible to have such a system and how would it be done?

Diagram showing what Epimetheus and Janus do.


texts: Do white dwarfs produce stellar wind? If not, why is that?

texts:
I've been told white dwarfs don't produce stellar wind like the sun produces solar winds. I don't quite understand why that is and can't really find any evidence that confirms or denies that.

My understanding is that solar wind is the product of the sun's variable magnetic field and consists of charged particles. Does nuclear fusion have to be occurring at the star's core for these charged particles to exist?


texts: How to analyse Jovian signal received at 20.1 MHz using dual dipole antenna?

texts:
I have purchased a Radio Jove kit and set it up. I have also received some signals. I am using Radio Skypipe II software as discussed in this Radio Jove tutorial (see also here) with a sound card to record and analyze the output of the receiver.

But what I get is like an image on the screen, which can be zoomed, and I'm not sure what I'm looking at.

What further process should I follow to make some analysis of Jovian radio signals at 20.1 MHz beyond just looking at the image (spectrogram? waterfall plot?) that the software produces?

Here is an example of the Radio Skypipe II output from their link:


texts: Number density of stars on the Galactic plane

texts:
The number density of stars (e.g. the number of stars per cubic parsec) is given by
$$N(z) = N(0) e^{-|z|/h}$$
where $z$ is the height above the Galactic plane, $h$ is the scale height for a specific component of the Galaxy, and $N(z)$ is the number density at different heights above the plane.

The scale heights for the thin disk and thick disks are:

Halo stars: $h=3\textrm{kpc}$
Thick disk: $h=1.5\textrm{kpc}$
Thin disk stars: $h=300\textrm{pc}$
Thin disk gas: $h=100\textrm{pc}$

Unfortunately I cannot find the values for the number density at the galactic plane: $N(0)$

Do you have any references in which I can find these numbers?


texts:
Media coverage of the "super worm equinox moon" (*eyeroll*) has stated that this is the last supermoon of 2019.  Since supermoons normally happen every three or four months, how can there be big gaps?

It feels like phenomena like supermoons, which are basically due to the relative phase of orbits, shouldn't have sharp transitions like this.


texts: Timekeeping on other celestial bodies than Earth

texts:
I have looked for months for any site capable of calculating solar altitude w.r.t an observer located on the surface of a generic celestial bodies, but with no luck as of now. Even NASA does not provide such information in its Horizons page/software, although technically Horizons contains all the needed data to calculate "local solar time"; indeed, Horizons allows asking for such an output... but currently output is jut "n/a" for bodies other than Earth:
*******************************************************************************
 Date__(UT)__HR:MN, , , L_Ap_Sid_Time,  L_Ap_SOL_Time,  L_Ap_Hour_Ang,
**********************************************************************
$$SOE
 2020-Aug-09 10:51,*,x,          n.a.,           n.a.,           n.a.,
 2020-Aug-09 11:51,*,x,          n.a.,           n.a.,           n.a.,

Url to ask for quantities 7, 34 and 42 (note: only 42 is declared as "Earth surface only").
https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27-85%27&CENTER=%27coord@301%27&OBJ_DATA=%27yes%27&MAKE_EPHEM=%27yes%27&TABLE_TYPE=%27OBSERVER%27&REF_PLANE=%27ECLIPTIC%27&COORD_TYPE=%27GEODETIC%27&SITE_COORD=%2723.4729700,0.67417634,0%27&START_TIME=%272020/8/9%2010:51%27&STOP_TIME=%272020/8/10%2010:51%27&STEP_SIZE=%271h%27&QUANTITIES=%277,34,42%27&FIXED_QUANTITIES=%27Custom%27&REF_SYSTEM=%27J2000%27&OUT_UNITS=%27KM-S%27&VECT_TABLE=%273%27&VECT_CORR=%27NONE%27&CAL_FORMAT=%27CAL%27&ANG_FORMAT=%27HMS%27&APPARENT=%27AIRLESS%27&TIME_TYPE=%27UTC%27&TIME_DIGITS=%27MINUTES%27&RANGE_UNITS=%27AU%27&SUPPRESS_RANGE_RATE=%27no%27&SKIP_DAYLT=%27no%27&EXTRA_PREC=%27yes%27&CSV_FORMAT=%27yes%27&VEC_LABELS=%27yes%27&ELM_LABELS=%27yes%27&TP_TYPE=%27ABSOLUTE%27&R_T_S_ONLY=%27NO%27&CA_TABLE_TYPE=%27STANDARD%27
So I tried to setup my own page ( http://win98.altervista.org/space/exploration/moon/moontime.html ), which makes its calculations starting from "colongitude" and moon terminator longitude, but it completely disregards observer latitude and altitude.
Any suggestion about pages which perform these calculations?

My GUI for NASA Horizons:
http://win98.altervista.org/space/exploration/NHUGUI.html
To specify a location on another body, write "coord@body" in "CENTER" field, without changing "COMMAND" field, which will be ignored, and write the triplet "lon, lat, alt" in field SITE_COORD.
To find predefined sites on a body use *@body , for example *@301 will list Moon landing aites.


texts: What will a lunar eclipse look like from moon? Will earth become a completely dark circle?


texts: If sun steals comets from other stars, then what is the primary source of comets?

texts: I heard some theory that sun may steal materials such as comets from neighbouring stars, is it true? But if is true, what is the primary source of those comets? Especially "who" creates them instead of steals them? And which stars are "willing" to bear our sun steals materials from it?


texts: Could we detect if Oumuamua asteroid wasn't an asteroid?

texts:
If Oumuamua wasn't an asteroid, could we detect that it is not an asteroid?

Disclaimer: I do NOT suggest that Oumuamua is in fact an alien spacecraft, a giant coffin, or a statue of Weird Al.

Since it apparently has a very unusual shape, if this is something else, with a different material (neither rock nor ice), could we detect that something is unusual?


texts:
Are there natural satellites in the Solar System that are geologically active? This includes volcanism, existence and motion of tectonic plates, et cetera.

Is it a common or a rather rare feature among such bodies?


texts: Why is right ascension measured on a 24 hour scale rather than a 23 hours and 56 minutes scale?

texts:
From several texts I have read, I have learned that right ascension is measured on a scale of 24 hours. I understand that Earth rotates almost exactly 360 degrees relative to distant objects, which is what RA is used for. The 24 hour system should only apply to the 361 degree rotation period (solar day). Why then do we split the sidereal day of the earth into 24 hours, when if it were split into 23 hours and 56 minutes we could know where an object would be x hours away after x hours?

More (possibly) relevant information:
I understand the Hour Angle HR is the measure of how far Aries is from the local meridian (RA of current meridian of longitude). This way you could calculate how many hours away the object is, but once again, this would not be exactly correct as 4 minutes has to be subtracted from the 24 hour scale, multiplying the whole time to something like 99.7% (14.44 degrees per hour), correct?

Thanks, this is really confusing me and I would appreciate some help. I did see a similar question but that had nothing to do with the sidereal day v. solar day issue I'm having.


texts: Which space telescope is the most distant?

texts: From the earth, and from the sun. Only interested in active, operational ones.


texts:
Sometimes at night you will look up to the stars and they will appear to twinkle, getting brighter and darker in bursts.

Why does this happen? Is this because of our atmosphere? Would they twinkle if you were just in space? How about looking from another planet in our solar system?


texts: Historical Lunar Tables and the Associated Error Bound

texts:
Consider as an example, AstroPixel's ``Six Millennium Catalog of Phases of the Moon''---
http://astropixels.com/ephemeris/phasescat/phasescat.html
My question is two-fold:

How are these tables which give (for example) dates and times of new moons and full moons to the nearest minute, generated?

How precise is this information? From http://astropixels.com/ephemeris/phasescat/phases0001.html
we see, for example, that on Jan 13 0001, a New Moon occurred at 10:58 (UT). How much of an error bound is there likely to be on these data?


texts: Which is the most early type star with a planet discovered by radial velocity method?

texts:
We have discovered planets in  Beta_Pictoris(A6V)here and Fomalhaut alpha(A3v)here.
However they were discovered by direct images.

There should be an stellar type limit by RV?
What is the most early type ever found?